Comprehensive Evaluation of Scotch Whisky Aroma Profiles Using SPME-GCxGC-TOFMS

Importance of the Topic

Scotch whisky is a high-value export product with complex aroma profiles that support consumer quality assessment and protect against fraud. With global trade exceeding £5 billion and strategic economic impact, detailed chemical characterization is essential for authenticity verification, process control, and regulatory compliance.

Objectives and Study Overview

This study aimed to apply solid-phase microextraction coupled with comprehensive two-dimensional gas chromatography and time-of-flight mass spectrometry (SPME-GCxGC-TOFMS) to unravel the complex aroma composition of a representative Glenfiddich Scotch whisky. Key goals included maximizing non-target compound detection, improving separation of coeluting species, and establishing confidence levels for compound identification.

Methodology and Instrumentation

Sample preparation involved loading 10 µL of neat whisky into vials, incubating at 60 °C, and extracting volatile species for 20 minutes with a DVB/CAR/PDMS fiber. Analysis was performed on a LECO Pegasus BT 4D GCxGC-TOFMS system equipped with a QuadJet thermal modulator. The first-dimension column was Rxi-5SilMS (30 m × 0.25 mm × 0.25 µm) and the second-dimension column was Rxi-17SilMS (1.3 m × 0.25 mm × 0.25 µm). Helium carrier gas flowed at 1.4 mL/min. The temperature program ramped from 50 °C to 280 °C, with a modulation period of 3 s. The TOFMS acquired full mass spectra (35–400 m/z) at up to 200 spectra/s. Retention indices were calibrated using C7–C30 alkanes.

Main Results and Discussion

The GCxGC contour plot revealed hundreds of distinct peaks across diverse polarity and volatility ranges. After filtering out interferences, 375 compounds were tentatively identified using spectral deconvolution, retention indices, and mass spectral library matching. Compounds were classified by retention index agreement (Match within ±10, Probable within ±20, Possible within ±30) and by spectral similarity thresholds (>800, 700–799, 600–699).

• 298 compounds (79.4 %) were confirmed matches by retention index
• 53 compounds (14.1 %) were probable
• 24 compounds (6.4 %) were possible candidates

Mass spectral similarity further reinforced confidence, with over 90 % of matches scoring above 700. Detailed contour and surface plots illustrated clear resolution of coeluting esters, alcohols, and lactones that would overlap in one-dimensional analyses. Fast acquisition rates and thermal modulation enabled advanced deconvolution to distinguish analytes from background noise and siloxane interferences.

Benefits and Practical Applications

The combined SPME-GCxGC-TOFMS approach delivers enhanced peak capacity, greater sensitivity for trace aroma components, and robust non-target screening. It supports quality control, authenticity testing, and flavor profiling in spirits, offering a reliable workflow for both research and industrial laboratories.

Future Trends and Opportunities

Emerging developments may include integration of machine-learning algorithms for automated deconvolution and compound classification, expansion of custom aroma libraries for Scotch whisky, and coupling with olfactometry for sensory correlation. Miniaturized modulation devices and higher acquisition rates promise further throughput improvements and real-time applications.

Conclusion

SPME-GCxGC-TOFMS on the Pegasus BT 4D platform provides comprehensive, high-confidence analysis of complex whisky aromas. The method outperforms traditional GC-MS by resolving coelutions, enhancing detection of low-abundance species, and delivering a time-efficient workflow supported by advanced software deconvolution.

References

No formal literature references were provided in the source document.